Mastering EKS Certificate Authority Rotation: Keep Your Cluster Secure

Certificate authority (CA) rotation is essential for keeping your Amazon EKS cluster secure and operational. It allows you to replace the CA before its validity period ends, ensuring that your cluster transitions to a successor CA without losing connectivity for any components. This proactive approach mitigates risks associated with an expired CA, which can lead to significant downtime and security vulnerabilities.

AWS automates the CA rotation lifecycle, updating all managed components in EKS, including the control plane and AWS Fargate, to trust the new CA. A critical aspect of this process is the dual trust period, where both the outgoing and successor CAs are trusted simultaneously. This ensures that your cluster remains operational while AWS distributes the successor CA across all components. If you don't append a successor CA yourself, AWS will do it for you as the outgoing CA nears expiration. Additionally, if you fail to activate the successor CA, AWS will automatically activate it before the outgoing CA expires, safeguarding your cluster's availability.

In production, be mindful of the dual trust period, as your cluster's trust bundle will contain two CAs, which can increase the size of your user data in EC2 launch templates. If you're near the 16 KB user data limit, consider compressing your user data using gzip to avoid issues. Remember that EKS clusters created since 2018 have CAs with a 10-year validity period, giving you ample time between rotations but still requiring proactive management to ensure security and connectivity.